Zinc ions prevent α-synuclein aggregation by enhancing chaperone function of human serum albumin

Metal ions present in cellular microenvironment have been implicated as drivers of aggregation of amyloid forming proteins. Zinc (Zn²⁺) ions have been reported to directly interact with α-synuclein (AS), a causative agent of Parkinson's disease and other neurodegenerative diseases, and promote its aggregation. AS is a small intrinsically disordered protein (IDP) i.e., understanding molecular factors that drive its misfolding and aggregation has been challenging since methods used routinely to study protein structure are not effective for IDPs. Here, we report the atomic details of Zn²⁺ binding to AS at physiologically relevant conditions using proton-less NMR techniques that can be applied to highly dynamic systems like IDPs. We also examined how human serum albumin (HSA), the most abundant protein in human blood, binds to AS and whether Zn²⁺ and/or ionic strength affect this. We conclude that Zn²⁺ enhances the anti-aggregation chaperoning role of HSA that relies on protecting the hydrophobic N-terminal and NAC regions of AS, rather than polar negatively charged C-terminus. This suggested a previously undocumented role of Zn²⁺ in HSA function and AS aggregation.